Field of the Invention
This invention relates to a circuit array substrate and a method of making the same and, more particularly, to a circuit array substrate for a display device configured to avoid causing multi-layered lines to break and/or malfunction and a method of making the same.
Display devices, such as liquid crystal display devices and plasma display devices, have been developed and put into practical use. Many display devices are provided with a circuit array substrate on which a plurality of signal and scanning lines are disposed in a matrix form.
An active-matrix type liquid crystal display device is described hereinafter by way of example of such display devices. The liquid crystal display device includes a pair of circuit array and counter substrates provided opposite to each other and a liquid crystal layer held, as a light modulation layer, in a gap between the array and counter substrates. The array substrate includes a glass substrate, signal and scanning lines disposed on the glass substrate in a matrix form, switching elements, e.g., thin film transistors (TETs) located in the vicinities of crossing portions of the signal and scanning lines, pixel electrodes connected to the TFTs, and an alignment layer coated on an upper surface of the lines, the TFTs, and the pixel electrodes. The signal and scanning lines are made of a low electric resistance material such as aluminum (Al) and molybdenum-tungsten (MoW), respectively. The pixel electrodes are made of a transparent conductive material such as indium tin oxide (ITO). The pixel electrodes are, however, made of a metal material such as Al for a reflection type liquid crystal display device.
There are storage capacitors formed by the pixel electrodes, their adjacent scanning lines, and an isolation layer disposed between the pixel electrodes and the scanning lines. The counter substrate also includes an ITO electrode on the inner surface of which an alignment layer is coated.
It is well known that the signal line is made of upper and lower laminated layers in which the former is the same ITO layer as the pixel electrode and the latter is a low electric resistance layer such as an Al layer provided on the ITO layer. The signal line is redundant in structure to maintain its conductivity even when either the ITO or Al layer is broken. Thus, independent photo-lithographic processes are necessitated for forming the ITO and Al layers, respectively. As a result, if the alignment of the ITO deviates from the Al layer between their independent processes, the storage capacitor defined between the signal line and the pixel electrode changes due to distance differences between them. As a solution of such change in storage capacitor, it may be considered that the ITO layer is made wider in width than the ITO layer to keep the distance substantially constant, no matter whether relative alignment deviations exist between the layers.
The inventor's experiment has revealed that the production yield still decreases resulting from breaking or malfunction of the signal lines even with such a structure set forth immediately above. According to further research made by the inventor, it has been found that such breaking or malfunction often takes place at the portions where the signal and scanning lines cross each other.